Pointer processing and path BIP-8 computation for large concatenated payloads

ABSTRACT

A system for performing Bit Interleaved Parity-8 (BIP-8) computation on large concatenated payloads, in a processing node of an optical communications networks. The BIP-8 computation system comprises storage means associated with each processing strip for allowing the comparison between calculated and transmitted frame error check values to be delayed.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 10/787,200, filed Feb. 27,2004, which is a divisional of application Ser. No. 09/663,823, filedSep. 15, 2000.

MICROFICHE APPENDIX

Not applicable.

TECHNICAL FIELD

The present invention relates to optical communication networks, and inparticular to performing pointer processing and path BIP-8 computationfor large concatenated payloads within processing nodes of such anetwork.

BACKGROUND OF THE INVENTION

Processing network nodes in current optical networks employing CMOStechnology are limited by the speeds of this technology, which are wellbelow currently available speeds of transmitting data over fibre opticlinks in such networks. In addition, at a network processing node, datamay come from several different sources, on different connections and atdifferent line clocks. However, at the node, all data must be processedat a local system clock. Accordingly, pointer processor systems are usedwithin processing network nodes to perform timing adjustments onincoming data, by converting the incoming data from a line clock domainto a local system clock domain or ‘shelf-time’ domain.

In order to be able to handle large data frames, pointer processorsusually comprise several integrated circuits. In turn, each integratedcircuit may comprise a plurality of processing strips, with eachprocessing strip having a limited data processing capacity. A knownpointer processor design for SONET (Synchronous Optical Network) or SDH(Synchronous Digital Hierarchy) type data frames is structured on STS(Synchronous Transmission Signal)-n level pointer processing strips,which are capable of processing the equivalent of n STS-1 buildingblocks from a SONET/SDH frame.

It is often desirable to be able to carry frames comprising largepayloads, such as concatenated STS-Nc frames across pointer processingnodes. This implies that for N greater than n, concatenated payloadsmust be carried across several STS-n level pointer processing strips andpossibly even across several chips, when the number of STS-n levelpointer processing strips on a single chip is insufficient for theSTS-Nc, when N is a large number. A SONET/SDH STS-Nc concatenated frameis built from N STS-1 building blocks pasted together, but informationabout the beginning of the SPE is kept only in the pointer bytes, H1andH2, of the leading STS-1 block in the concatenation. In other words,only the leading STS-1 block in a concatenation comprises valid pointerinformation within its H1 and H2 bytes, whereas the H1 and H2 bytes ofthe trailing STS-1 blocks of the concatenation contain only aconcatenation indication. On the other hand, in processing a SONET/SDHframe on a pointer processing strip, the strip must have valid pointerinformation for all the STS-1 blocks within the processed frame. Itfollows that in processing a concatenated payload across several pointerprocessing strips, strips processing trailing STS-1 blocks in theconcatenation must obtain the valid pointer information from the stripprocessing the leading STS-1 block in the concatenation.

FIG. 1 illustrates a general scheme of passing pointer informationthrough a pointer processing strip or SYNC block, such that it canoperate properly on SONET/SDH type data frames. The pointer processingstrip has a pointer interpreter side and a pointer generator side. Thepointer interpreter side, working in the line clock domain, receives theincoming data frames on the ‘Data-in’ line, interprets their overheadand writes (W) the payload in an Elastic Store. The pointer generatorside, working in the system or shelf clock domain, reads (R) the payloadfrom the Elastic Store and forms new SONET/SDH or other type frames tobe passed further to the processing node on the ‘Data-out’ line. Thegeneration of frames by the pointer generator side is based on a SYNC 8Ksignal, which is an 8 kHz reference indicating the phase of the frame tobe formed. The writing and reading of the payload to and from theelastic store, respectively, must be done based on corresponding validpointer information. In addition, due to the format of the SONET and SDHtype frames, valid pointer information on either side of the pointerprocessor must be available before the reading of the H3 overhead byte,on the pointer interpreter side, or the generation of the H3 byte on thepointer generator side. This is due to the fact that the H3 byte, whichfollows the H1/H2 pointer bytes in the line overhead of the SONET/SDHstandard, may, in the event of a negative pointer adjustment, be part ofthe actual SPE payload. Let A and B be ports of inputting pointerinformation to the pointer interpreter and the pointer generator sides,respectively, from a previous pointer processing strip, for example.Also, let A′ and B′ be corresponding ports of outputting pointerinformation. Considering the pointer processing of a certain frame, lett₁ be a moment in time when the H3 byte is read from the incoming dataand t₂ be a subsequent moment in tine when the H3 byte is added to thegenerated frame, according to the SYNC 8K signal. According to theabove, it follows that for the pointer processing strip to functionproperly, valid pointer information must be available at A before t₁ andat B before t₂. Furthermore, if this condition is met and letting Δt bethe propagation delay of pointer information through the pointerprocessing strip, valid pointer information will be outputted at A′ onor before t₁+Δt, and at B′ on or before t₂+Δt.

FIG. 2 illustrates a known scheme of passing pointer information along asequence of pointer processing strips or SYNC blocks #1, #2, #3, etc.Data come in simultaneously at all blocks on their pointer interpretersides, through ‘Data-in’ lines. Likewise, data is generated on the‘Data-out’ lines based on the same SYNC 8K signal running to all threeblocks. Assuming that SYNC block #1 receives valid pointer informationthrough A and B at t₁ and t2, respectively, then SYNC block #2 receivesthe valid pointer information from SYNC block #1, at t₁+Δt and t₂+Δt,respectively, SYNC block #3 receives the valid pointer information att₁+2Δt and t₂+2Δt, respectively, and so on In order for the SYNC blocksto operate properly, the incoming H3 bytes must be read as follows: onor after t₁ on SYNC block #1, on or after t₁+Δt on SYNC block #2, on orafter t₁+2Δt on SYNC block #3, and so on. Similar conditions apply tothe outgoing H3 bytes in the generated frames. It follows that in thisdesign, only a limited number of pointer processing strips can be usedto perform pointer processing on a concatenated payload. Specifically,the number of strips that can be used is approximately equal to T/Δt,where T is the length of the critical time region during which thepointer information must be propagated. Specifically, this critical timeregion is defined by the time period between the moment when all thenecessary pointer information on the strip is available, such as afterthe H1/H2 bytes of the last STS-1 leader on the strip has been read, andthe moment when all the pointer information must be available on thenext strip, which is the moment of processing the H3 byte of the firstSTS-1 block processed on that strip. In the SONET standard T isapproximately 100 nanoseconds (ns). Δt is dependent on the technologyand is currently of the order of several ns, depending on the capacityof the SYNC blocks. For example, one of the technologies currently ownedby the assignee of this application, features a 25 ns pointerinformation propagation delay between STS-48 level processing strips.This implies that a concatenated payload cannot be carried across morethan 4 such strips, limiting the size of the concatenation frame to anSTS-192c.

In addition to the need for conveying pointer information downward fromone SYNC block to the next, along a string of SYNC blocks spanning aconcatenated payload, information must also be conveyed in an upwardfashion. For example, when the pointer state of an STS-1 block withinthe concatenation is ‘AIS’ (alarm indication signal), instead of ‘V’,for valid pointer or ‘C’ for concatenation indicator, such informationis transmitted to preceding STS-1 blocks. From the information thattravels upward across slices as indicated by the arrows U, especiallyimportant are frame error check values such as the B3 byte data, ofwhich computation is commonly performed within the pointer processors.In the SONET standard B3 is a path Bit Interleaved Parity-8 (BIP-8)byte. The value of a B3 byte in a given frame is calculated by XOR-ingthe SPE bytes of the given frame starting with the J1 byte. Thecalculated B3 value for the given frame must be checked against atransmitted B3 value for the given frame, which is located within theframe following the given frame in the transmission.

For a concatenated frame, the B3 value for the entire frame is kept inthe B3 byte position of the leading STS-1 block in the concatenation andit is also calculated through an XOR operation over all SPE bytes in theframe. This calculation can be accomplished by XOR-ing the B3 values ofall the STS-1 blocks in the concatenation. Accordingly, when aconcatenation is split across several pointer processing strips, the B3byte data must be sent upwards from strip to strip, until the stripcontaining the leading STS-1 block of the concatenation is reached.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a novel pointer processingsystem and method for carrying large concatenated payloads across aprocessing node of an optical communications networks.

It is another object of the invention to provide a novel system andmethod for BIP-8 computation for large concatenated payloads within aprocessing node of an optical communication network.

According to one aspect of the invention, there is provided a pointerprocessor system comprising: an input port for receiving input data, aparallel array of pointer processing strips, for adjusting line clockdomain input data to system clock domain output data, means fordistributing input data from the input port to the pointer processingstrips according to a distribution order, a pointer interpreter delayblock controlling input data reading on at least a pair of an i^(th) andj^(th) pointer processing strips, such that corresponding input data isread on the j^(th) pointer processing strip after a predeterminedpointer interpreter pair delay from a time moment when correspondinginput data is read on the i^(th) pointer processing strip, wherein i andj are integers assigned to the pointer processing strips according tothe distribution order and j is greater than i, means for collectingoutput data from the pointer-processing strips according to a collectionorder, and an output port for transmitting output data.

According to another aspect of the invention, in a digital opticalnetwork, a method of performing pointer processing on a concatenatedpayload is provided. The method comprises the steps of distributing theconcatenated payload into a plurality of data slices according to adistribution order and performing pointer processing operations on atleast a pair of an i^(th) and j^(th) data slices. The pointer processingstep is performed such that pointer processing of a fixed byte withinthe j^(th) data slice is performed after a predetermined pair delay fromthe pointer processing of a corresponding fixed point in the i^(th) dataslice, wherein i and j are integers assigned to the pointer processingstrips according to the distribution order and j is greater than i.

According to a further aspect of the invention, there is provided a BitInterleaved Parity-8 (BIP-8) computation system. The BIP-8 computationsystem comprises a frame error check value computation block receivingfist frame data from a frame processor, for computing new first frameBIP-8 values, storage means receiving second frame data from the frameprocessor for storing old first frame BIP-8 values, wherein the oldfirst frame BIP-8 value is transmitted within the second frame, acomparator circuit receiving data from the BIP-8 computation block, fromthe storage means and from a critical time signalling circuit, forcomparing the new first frame BIP-8 values with the old first frameBIP-8 values. The critical time signalling circuit sends an enablingsignal to the comparator, for enabling the comparison operationaccording to a predetermined comparison timing schedule.

According to yet a further aspect of the invention there is provided amethod of computing a local frame error check values for a data slice ofa transmission frames processed at nodes of a digital optical network.The method comprises computing a calculated local frame error checkvalue based on frame values received within a first transmission frame,storing a transmitted local frame error check values received within asecond transmission frame; and comparing the calculated local frameerror check value and the transmitted local frame error check value uponthe reception of a comparison signal.

According to yet a further aspect of the invention, there is provided apointer processor system for performing pointer processing on a largeconcatenated payload across multiple integrated circuits. The pointerprocessor system comprises a first integrated circuit, a secondintegrated circuit having a common chip boundary with the firstintegrated circuit an array of pointer processing strips for performingpointer processing functions, wherein the pointer processing strips aredistributed on the first and second integrated-circuits, a firstinter-chip communication block located on the first integrated circuitnear the common chip boundary and a second inter-chip communicationblock located on the second integrated circuit near the common chipboundary, for collecting information from pointer processing stripslocated on the first integrated circuit to pointer processing stripslocated on the second integrated circuit across the common chipboundary.

According to yet a further aspect of the invention there is provided amethod of performing pointer processing on a concatenated payload acrossmultiple integrated circuits, within a digital optical network. Themethod comprises distributing the concatenated payload into a string ofdata slices according to a distribution order, determining anacross-chip pair of data slices within said string, wherein theacross-chip pair comprises data slices requiring pointer processing onseparate integrated circuits and transmitting pointer information from afirst data slice in the across-chip pair to a second data slice in theacross-chip pair. The transmission of the pointer information includesdividing the pointer information into a non-critical set and a criticalset, transmitting the non-critical set of pointer information away froma critical region, serially and transmitting the critical set of pointerinformation within the critical region, asynchronously.

Among the advantages presented by the pointer processing method andsystem of the preferred embodiments of the invention is the ability toperform pointer processing and BIP-8 computation on very largeconcatenated payloads. Other advantages, objects, and features of thepresent invention will be readily apparent to those skilled in the artfrom a review of the following detailed description of preferredembodiments in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be explained, by way of example only,with reference to certain embodiments and the attached Figures in which:

FIG. 1 illustrates a block diagram of a general pointer processingstrip;

FIG. 2 illustrates a block diagram of a known pointer processing systemcomprising several pointer processing strips;

FIG. 3 illustrates a block diagram of a pointer processing systemaccording to an aspect of a first embodiment of the invention;

FIG. 4 illustrates the delay in the processing on two pointer processingstrips such as in FIG. 3;

FIG. 5 illustrates a block diagram of a pointer processing systemaccording to a further embodiment of the present invention;

FIG. 6 illustrates a fig diagram for a B3 computation system accordingto another embodiment of the present invention;

FIG. 7 illustrates a block diagram of a B3 computation system accordingto another embodiment of the present invention;

FIG. 8 illustrates a block diagram of an across-chip communicationsystem according to another embodiment of the present invention; and

FIG. 9 illustrates a flow chart of a method of communicating informationacross chip according to another embodiment of the present invention;

Similar references are used in different drawings to denote similarcomponents.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

FIG. 3 illustrates a block diagram of a pointer processor machine 10according to an embodiment of a first aspect of the present invention.The pointer processor machine 10 comprises an input port 12, a parallelarray of N pointer processing strips or SYNC blocks 14, means fordistributing input data 16, a delay block 18, means for collectingoutput data 20 and an output ports 22.

The input port 12 receives input data in a line clock domain. The inputdata is distributed to the parallel array of pointer processing strips14 by the means for distributing data 16, according to a distributionorder (DO), such as the standard SONET/SDH transmission order forSONET/SDH frames. Given the distribution order, the pointer processingstrips 14 can be numbered from 1 to N, where the 1^(st) strip receivesthe leading segments or data slices of a data frame and the Nth stripreceives the end data slices of a data frame. The means for distributingdata or distribution block 16 comprises a Time Slot Interchange (TSI)block which arranges the STS-1 block in the frames arriving at thepointer processor system 10 in the format required at the pointerprocessing strips 14.

The parallel array of pointer processing strips 14 adjust input data ina line clock domain to output data in a system clock domain. Eachpointer processing strip 14 in FIG. 3 is similar to the one shown inFIG. 1, comprising a Pointer Interpreter, an Elastic Store and a PointerGenerator in order to perform the pointer processing function. Thepointer processing strips 14 may be STS-12, STS-24, or STS-48 levelpointer processing strips or the like. In the case where incoming datacomprises large concatenated SONET/SDH frames, these are distributedacross several SYNC blocks and pointer information is transmitted alongthe sequence of these blocks, from one to the next.

The data adjusted from the line clock domain to the system or shelfclock domain by the pointer processing strips 14, is collected by themeans for collecting data 20 according to a collection order (CO), whichis usually the same as the distribution order (DO), since usually theobjective is to have the payload run smoothly through the pointerprocessor. The collection of data from the pointer processing strips 14and generation of a new SONET, SDH or other type of frame, carrying thesame payload as the incoming frame, but being adjusted to the shelf sideclock, is governed by a SYSTEM 8K signal. The means for collecting data20 usually comprise a TSI block performing a mirror image operation tothe TSI block operation within the means for distributing data 16.

The data at the system clock domain, collected from the pointerprocessing strips 14 by the means for collecting data 20 is outputthrough the output port 22 and transmitted to the system processing nodefor further processing.

According to an aspect of the present invention, the delay block 18controls data processing on least two pointer processing strips 14, saythe i^(th) and the j^(th) blocks, where j is greater than i. The delayblock 18 ensures that data processing on the second processing strip isdelayed from data processing on the first processing strip by apredetermined pointer pair delay, Δt. In the embodiment in FIG. 3, thedelay block 18 is shown as controlling data on the pointer interpreterside of the SYNC blocks 14. In this case, the pair delay may be morespecifically referred to as a pointer interpreter pair delay. However,the delay block 18 could similarly control data only on the pointergenerator side of the SYNC blocks 14, by introducing pointer generatorpair delays. In the preferred embodiment described in detail later on,delay blocks control data processing in both the pointer interpreter andpointer generator sides of the SYNC blocks 14.

FIG. 4 illustrates the delay in processing data slices on the i^(th) andj^(th) strips, relative to a corresponding clock signal CLK. The clocksignal may represent either the line clock or the shelf clock, dependingon which side of the elastic store the delay is implemented. Since dataslices processed on the i^(th) and j^(th) strips have fixed formats, thepredetermined pair delay Δt is illustrated as a delay in processing acorresponding fixed points, such as the H2 bytes, on each strip. Inaddition, since the operation is digital, the predetermined pair delayΔt is measured in time slots or clock cycles of the clock signal CLK. Inthe embodiment illustrated in FIG. 4, the predetermined pair delay Δt isset at 2 clock cycles.

The delay block 18 is preferably implemented as a software programmabledelay. In addition, the delay block 18 could be implemented as a singlehardware entity, or within the means for distributing data 16, or withinthe pointer processing strips 14, as a First In First Out (FIFO)register, for example. A specific embodiment found preferable the pointof view of hardware overhead, contemplates implements the delay blockfunction within a framer circuit (not shown), which also incorporatesthe means for distributing data 16 to the pointer processing strips 14,involves less hardware overhead.

FIG. 5 illustrates an array of parallel pointer processing strips 14 ona pointer processing machine 10 such as in FIG. 3, operating accordingto a preferred embodiment of the invention. In the embodimentillustrated in FIG. 5, a delay block 18′ controls all data entering thepointer processing strips 14 on the pointer interpreter (PI) or elasticstore (ES) writing (W) sides. Moreover, a similar delay block 18″controls all data exiting the pointer processing strips 14 on thepointer generator (PG) or elastic store reading (R) sides, in a similarfashion. According to the preferred embodiment, any two adjacent pointerprocessing strips 14 feature relative pair delays Δt on both the inputand output lines, with the first of the two processing strips 14 in theadjacent pair processing earlier. A staggering effect of the array ofpointer processing strips 14 is achieved. The delays on the pointergenerator (PG) sides are achieved by delaying the SYNC 8K based signalsrunning to each strip.

Furthermore, according to the preferred embodiment, the pair delay Δtbetween any two adjacent pointer processing strips 14 is approximatelyequal to the pointer information propagation delay between two suchadjacent pointer processing strips 14, when they are located on the sameintegrated circuit. This arrangement overcomes the limitation of thesystem described in the background section, in which a restricted numberof parallel pointer processing strips 14 could be used in carrying aconcatenated frame, where the restriction was caused by the accumulationof propagation delays in passing pointer information downward, fromstrip to strip. In fact, with respect to the downward pointerinformation propagation, the system illustrated in FIG. 5 poses norestriction. In theory, an infinite number of pointer processing strips14 could be used in carrying a concatenated payload, as long as thestrips 14 are on the same integrated circuit. However, in practice, anintegrated circuit may include only a limited number of pointerprocessing strips 14, and solutions to problems associated with the needto cross chip boundaries will be described later. In addition, asmentioned in the background section, in carrying a concatenated payloadacross parallel pointer processing strips 14, communication amongpointer processing strips spanning the concatenation also takes place ina upward fashion. Solutions to problems associated with this type ofcommunication, are also described below. Nonetheless, the systemdescribed in connection with FIG. 5, advantageously allows very largeconcatenated payloads to be carried across a pointer processor.

For example, a current technology owned by the assignee of the presentinvention, employs pointer processor machine comprising ApplicationSpecific Integrated Circuits (ASIC's) that include eight STS-48 levelpointer processing strips, featuring a pointer information propagationdelay from strip to strip of 25 ns. Therefore, employing the preferredembodiment previously described in reference to FIG. 5 with Δt=25,concatenated payloads could be easily carried on as much as 8 suchpointer processing strips. This is equivalent to an STS-384c, which isdouble in size to the STS-192c supported by the system described in thebackground section.

Path BIP-8 Computation for Large Concatenated Payloads

FIG. 6 illustrates, by way of example, a timing diagram in connectionwith a method of performing the B3 calculation and error detectionacross a system of six STS-48 level pointer processing strips, locatedall on the same ASIC and arranged according to the embodimentillustrated in FIG. 5. The timing diagram illustrated may equally welldescribe the process on the Elastic Store Write sides of the strips, oron the Elastic Store Read side of the strips. The pointer processingstrips are staggered with a pair delay Δt, such as in FIG. 5. Assumethat a concatenated payload is carried across all six strips, with thefirst strip spanning the concatenation being strip # 1. The B3calculation for the concatenated payload comprises calculating local B3values for each strip, starting on the last strip, and propagating thesevalues upwards on the array, along the B3 propagation path, up to thefirst strip.

Usually, the local B3 value on a strip is calculated continuously, byXOR-ing all SPE bytes read on the strip. The J1 byte marks the beginningof the SPE bytes for a new frame, hence the local B3 calculationcorresponding to a first frame F1 is correct, i.e. takes into accountall SPE bytes for F1 read on that strip, just before the arrival of theJ1 byte for the next frame, F2.

Accordingly, the J31 byte for F2, on the last strip spanning theconcatenation, i.e. strip #6 in this case, marks the beginning of the B3propagation path, for F1. The shape of the B3 propagation path is givenby the staggering of the strips with Δt and by the B3 upward propagationdelay Δt′ from strip to strip. On arriving at each strip, the B3 valuereceived from below along the B3 propagation path is sampled, combinedwith the B3 value for the local strip into a new B3 value to be launchedfurther along the B3 propagation path. This process ends with a newcalculated B3 value on the first strip spanning the concatenation. ThisB3 value is the B3 calculated value for the entire F1.

For detecting frame errors, a B3 value for F1 transmitted within F2,must be compared with newly calculated B3 for F1. However, the B3 for F1calculation performed as above may not finished at the time ofextracting the transmitted B3 for F1 from the corresponding F2 data readon strip #1. To overcome this timing problem, the transmitted B3extracted from F2 on strip #1 is saved in some storage means such asregister 35. The comparison of the calculated and transmitted B3 valuesfor F1, can thus be performed after the reading of the transmitted B3value from F2.

In general, if a concatenated frame spans n strips on the same ASIC, thetime length of the B3 propagation path, or the time when the B3calculation is available at the first strip, is:T _(B3)=(n−1)*Δt+(n−1)*Δt′=(n−1)*(Δt+Δt′)

In the above embodiment, the calculation of B3 for F1 must be availableat the first strip before the beginning, i.e. the J1 byte, for the framefollowing F2, say F3. The available time for B3 to reach the first stripis thus T_(B3)av=length of time. For SONET/SDH frames, the length offrame is 125 microseconds.

This reduces the number of strips on the same ASIC, available to carry aconcatenated payload to n=T_(B3)av/(Δt+Δt′)+1. In order to overcome sucha limitation, a pipe of R registers for saving values of B3 onconsecutive frames, rather than a single register for saving a single B3value, may be implemented, as one skilled in the art would easilyappreciate. In such a case, the time available becomes T_(B3)av(R)=R*length of frame, and the number of strips, on the same ASIC, that canbe used is: n=R *length of frame/(Δt+Δt′)+1. Since R is unrestricted, nbecomes restricted only by the number of strips that can be fitted onthe same ASIC.

FIG. 7 illustrates by way of example a functional block diagram of asystem for computing a frame error check value 40, in, accordance withan aspect of the present invention. In the example in FIG. 7, the frameerror check value is a BIP-8 value. Extending the concepts illustratedin this example to other frame error check values will be easilyappreciated by those skilled in the art.

The BIP-8 computation system operates on the i^(th) pointer processingstrip 14 from an array of pointer processing strips 14, such as in FIG.5, for example. Accordingly, the system processes the i^(th) data slicefrom a possibly larger frame structure. The data processed on the i^(th)strip is part of consecutive incoming frames, such as a first frame F1and a second frame F2. To detect errors based on BIP-8 values, locallycomputed BIP-8 values for F1 must be compared with a transmitted BIP-8values for F1, which arrives within F2 data. For simplicity, the systemillustrates an F1 data block 42 and an F2 data block 44 as separateentities, although F1 data and F2 data arrive within a single physicalentity. Each data block comprises n STS-1 data blocks, where n is theSTS capacity level of the processing strip comprising the BIP-8computation system 40. The computed BIP-8 values for F1 are calculatedwithin a computed values block 46, based on F1 data inputs. Thetransmitted BIP-8 values for F1 arrives within the next frame, F2,therefore in the F2 data block 44, and are inputted for storage in antransmitted values storage block 35, corresponding to the register 35 inFIG. 6. The transmitted BIP-8 values are stored for delaying thecomparison with the computed values, preferably until the computation ofthis later value(s) is completed in time. The computed values and thetransmitted values are compare by a COMPARE block 48, at the indicationof critical time signal, sent by a critical time block 50.

The critical time block usually signals the time of arrival of a newframe, for which no storage means 35 for the corresponding transmittedBIP-8 values would be available. For example, in the case of checking B3byte data, if storage means are provided only for storing the B3 valueon F2, the critical time block will trigger the comparison before thearrival of the J1 byte for a third frame F3. As mentioned previously inreference with FIG. 6, the delay available from the reading of thetransmitted frame error check value(s) such as B3, until the comparisonwith the corresponding calculated value(s) can be increased byimplementing a pipe of storage registers for the transmitted value(s),with one set of registers corresponding to a frame.

For the B3 processing, in particular, the calculation of the B3 valuesfor the i^(th) data slice, implies computing contents for the n B3blocks 43 for each STS-1 block in the F1 data block (42), by XOR-ing theSPE bytes in each STS-1 block. The n B3 values are further combined inthe calculated B3 values for the calculated values block 46, based onthe concatenation state of each of the STS-1 block, as indicated withinthe H1/H2 bytes of each of these blocks, as well as based on informationincoming from the i+1 strip or data slice. The number of B3 calculatedvalues corresponds to the number of valid pointers (VPTR) contained inthe H1/H2 bytes of the STS-1 blocks.

The B3 values transmitted within the F2 data block, for F1, are storedonly for the STS-1 blocks comprising valid pointer (VPTR) within theirH1/H2 bytes, as only those B3 values need comparison. The number as wellas the values of the calculated and transmitted B3 values must match;otherwise an error indication is generated.

If the data processed on the if strip is part of a concatenationstarting in an earlier strip, this information is contained in the H1/H2byte, which, in such case, contains a concatenation indicator.Furthermore, in such case, the calculated B3 value for the data on stripi that is part of a concatenation carried on both strip i and strip i−1is transmitted from the calculated value(s) block to a B3 block on stripi−1. A preferred implementation is to transmit:

a) when the STS-1 block in the F1 data block contains a concatenationindicator in its H1/H2 byte, a positive concatenation signal to the CONCblock on strip i−1, and the B3 calculated value corresponding to theSTS-1 #1 on the strip to the B3 block on strip i−1;

b) when the STS-1 block in the F1 data block contains a VPTR in itsH1/H2 byte, a negative concatenation signal to the CONC block on stripi−1 and B3=00 to the B3 B3 block on strip i−1;

Strip i receives similar signals from CONC block and the B3 block on thei+1 strip, as it sends itself to the CONC block and the B3 block on thei−1 strip. Therefore, all pointer processing strips 14 in an array canbe identical with respect to the BIP-8 computation function, whichadvantageously simplifies the design of the pointer processor machine10.

Across-Chips Communication Techniques

FIG. 8 illustrates an across-chip communication system 70 forcommunication of information across-chip, along an array of pointerprocessing strips of a pointer processor. Information along pointerprocessing strips located on the same ASIC may be carried using thesystem and methods described above, in reference with FIGS. 3 to 8. Inaccordance with another aspect of the present invention, the across-chipcommunication system 70 comprises at least two inter-chip communicationblocks 72, with one inter-chip communication block 72 located on eachside of a chip boundary. Data travels along the array pointer processingstrips 14 in an upward and downward fashion, from one strip 14 to theadjacent ones, for strips located on the same ASIC, or from a strip 14to the inter-hip communication block 72 on the same ASIC as the strip14, for strips 14 located near the chip boundary.

Downward Propagation of Pointer Information

On a pointer processing strip, a critical region for passing pointerinformation can be defined as the time region the processing of the H2byte of the last STS-3 leader on the strip, e.g. the 10^(th STS-)1 blockfor an STS-12 level strip, and the processing of the first H3 byte, i.ethe H3 byte of the first STS-1 block on the strip, within the sameframe.

Accordingly, the pointer information that must be communicated acrossslices spanning a concatenated frame can be divided into non-criticalinformation, which can be passed away from a critical region, andcritical information, which can only be determined and therefore furthercommunicated to another strip, within the critical region. Thenon-critical pointer information comprises data such as pointer value,Elastic Store Write Address (ES_Waddr), Elastic Store Read Address(ES_Raddr) and so on. However, a characteristic of the non-criticalinformation values is that their value during the critical region can beinferred from their value at any other point in the frame, provided theoffset of that other point from the critical region is known.

The critical information comprises p-stuff and n-stuff indications, andthe like. Critical information signals can only be determined, on astrip, during the critical region.

FIG. 9 illustrates a flow chart for a method of passing pointerinformation across a chip boundary, from one pointer processing strip toanother. The method comprises an initial step 100 of dividing thepointer information into a critical set and a non critical set,according to the defined critical region. Following, the methodcomprises the step 110 of serializing data buses comprising non-criticalinformation, followed by the step 120 of passing the serializednon-critical data synchronously, away from the critical region. Thepassing of information away from the critical region implies that datatransfer occurs before the time occurrence of the critical region. Inaddition, the non-critical data which is passed synchronously, shouldpreferably be passed at low frequencies, in order to guard againstcircuit board delays and thus ensure reliability of transmission. Duringthe critical region, two operations are performed. At step 130, thereceived non-critical information is adjusted to correspond to the timeof critical region. At step 140, the critical data is passedasynchronously in single bit buses.

For example, the transmission of the Elastic. Store Write address(ES_Waddr), a non-critical signal, from processing strip i to processingstrip i+1, across a chip boundary, occurs as follows within a preferredembodiment:

a) During the A1 byte time slot, the ES_Waddr is sampled on strip i;

b) The sampled value, which is 6 bits wide, is serialized, andtransmitted across the chip boundary, to strip i+1, through theinter-chip communication line designated to passing ES_Waddr,

c) On strip i+1, the received ES_Waddr is adjusted as follows:

New ES_Waddr=[Received ES_Waddr+4×87] mod ES size, where ES is theElastic Store size. The 4×87 offset factor is due to the fact that thereare 4×87 SPE bytes between the A1 byte and the beginning of the criticalregion.

Non-critical information comprises single bit buses, such as AISindication, as well as all multiple bit buses, such as Elastic StoreWrite address. According to a preferred embodiment, the passing ofmultiple bit buses is done serially at a low frequency, in order toincrease reliability of the communication. Critical informationcomprises only single bit buses. Within the preferred embodiment, singlebit buses, both critical and non-critical, are passed asynchronouslyfrom ASIC to ASIC.

Upward Propagation of Frame Error Check Data

The process of upward propagation of information is described, by way ofexample, with reference to the process of propagating B3 data The B3signals require information regarding the beginning of the SPE. As such,B3 values are transmitted only during the payload and their transmissiontime from chip to chip varies with respect to where the chip is locatedin a string of chips. Thus, if there are N chips, the B3 from the chip Nto the N−1 will happen at a time Δt after J1, from N to N−1 thetransmission will take place at Δt+Δt′ to account for propagation delayof B3 through N−1 chip, and so on.

Numerous modifications, variations and adaptations may be made to theparticular embodiments of the invention described in the documentsattached herein, without departing from the scope of the invention,which is defined in the claims.

1. A bit Interleaved Parity-8 (BIP-8) computation system comprising: aframe error check value computation block receiving first frame datafrom a frame processor, for computing new first frame BIP-8 values;storage means receiving second frame data from the frame processor forstoring old first frame BIP-8 values, wherein the old first frame BIP-8value is transmitted within the second frame; and a comparator circuitreceiving data from the BIP-8 computation block, from the storage meansand from a critical time signaling circuit, for comparing the new firstframe BIP-8 values with the old first frame BIP-8 values, wherein thecritical time signalling circuit sends an enabling signal to thecomparator, for enabling the comparison operation according to apredetermined comparison timing schedule.
 2. The BIP-8 computationsystem in claim 1, where the BIP-8 values are B3 parity check bytes.